a. Field of the Invention
The present invention relates to methods and apparatus for locating the fossa ovalis, as well as methods and apparatus for performing transseptal punctures.
b. Description of Related Art
The transseptal puncture for left atrial and left ventricular catheterization was initially described simultaneously by Ross and Cope in 1959. In the 1960s, Brockenbrough and colleagues modified the design of the transseptal needle and the guiding catheter. In the late 1960s and 70s, its use declined because of the occurrence of complications and because of the development of selective coronary arteriography which led to the refinement of catheterization of the left side of the heart by the retrograde approach. With the advent of percutaneous balloon mitral valvuloplasty, antegrade percutaneous aortic valvuloplasty as well as catheter ablation of arrhythmias arising from the left atrium (or utilizing left sided bypass tracts), the transseptal puncture technique for access to the left atrium and ventricle has made a strong comeback.
The goal of transseptal catheterization is to cross from the right atrium to the left atrium through the fossa ovalis. Mechanical puncture of this area with a needle and catheter combination is required for the procedure. Typically, a guidewire is inserted through the right femoral vein and advanced to the superior vena cava. A sheath (typically about 66 cm long) is placed over a dilator (typically about 70 cm long) that is advanced over the guidewire into the superior vena cava. The guidewire is then removed and a 71 cm Brockenbrough needle is advanced up to the dilator tip. The apparatus is dragged down into the right atrium, along the septum. When the dilator tip is positioned adjacent the fossa ovalis (sometimes determined under ultrasound guidance), the needle is then pushed forward so that it extends past the dilator tip, through the fossa ovalis into the left atrium. The dilator and sheath may then be pushed through the fossa ovalis over the needle. The dilator and needle are then removed, leaving the sheath in place in the left atrium. Thereafter, catheters may be inserted through the sheath into the left atrium in order to perform various necessary procedures.
The danger of the transseptal approach lies in the possibility that the needle and catheter will puncture an adjacent structure such as the aorta, the coronary sinus or the free wall of the atrium. In the Cooperative study on Cardiac Catheterization, a 0.2% mortality rate, 6% incidence rate of major complications and 3.4% incidence of serious complications were reported including 43 perforations. To minimize this risk, the operator must have a detailed familiarity with the regional anatomy of the atrial septum. Due to the potentially life threatening complications of the procedure, many operators feel that fluoroscopy, which at best represents an epicardial shadow of the heart, is not enough and additional tools are needed. Additional techniques which may be used to locate the fossa ovalis include biplane fluoroscopy, pressure manometry, contrast infusion as well as surface, transesophageal or intracardiac echocardiography (i.e., ultrasound).
While echocardiography can be useful, there are potential problems in using these techniques to locate the fossa ovalis. Contact of the transseptal dilator and the tenting of the membrane of the fossa ovalis that one looks for with echo guidance may be missed depending on the area of the fossa that is cut by the ultrasound beam. If a different portion of the membrane is tented by the dilator tip, this may not be apparent in the ultrasound picture. If transesophageal echocardiography (TEE) is used to guide the puncture, a different operator has to operate the TEE system and therefore errors can occur especially in the interpretation of the data. For example a different catheter (other than the transseptal dilator) may be tenting the fossa. Cardiac tamponade and other complications are known to have occurred during transseptal punctures performed in electrophysiology laboratories despite the routine use of ultrasound guidance. The placement and use of ultrasound catheters also often require the insertion of large intravascular sheaths. The additional time and expense that the use of ultrasound catheters and sheaths incurs is not inconsiderable and this can make it impractical to use them routinely.